This invention relates to continuous jet, ink jet printers typically used for industrial purposes to mark products with bar codes, date codes and other important information. Continuous jet ink jet printers are well known in this art and will not be described in detail in this specification. For background, the reader is referred to Diebold et al. U.S. Pat. No. 4,121,222 hereby incorporated by reference. In brief, an ink jet printer of this type supplies ink to a nozzle which is typically stimulated by a piezoelectric device causing a stream of ink, emitted from an orifice formed in the nozzle to break-up into discrete droplets. At the point of break-up, a charge ring or similar device is provided to selectively charge drops which are desired to be deflected onto the substrate or product to be marked. Not all drops are so charged and the remaining drops pass to a gutter or recovery device which circulates the uncharged drops back to the ink supply system for reuse.
Clogging of continuous jet printers can be a problem, particularly when small orifices are utilized for high precision printing. In an effort to reduce clogs, nozzles are fabricated under clean room conditions in an attempt to ensure that particles and debris are not deposited in the nozzle or in the supply conduit which bring ink to the nozzle. In the ink supply system, filters are usually employed in an effort to catch impurities which may remain in the ink or which may form in the ink during operation of the system. Nevertheless, clogs do occur for various reasons. For example, the drop charging process can cause precipitation of ink dyes in the vicinity of the nozzle orifice. Over time, these deposits may clog the nozzle.
Efforts at unclogging nozzles are known in this art. In particular, nozzles having both an inlet and an outlet have been employed as disclosed, for example, in U.S. Pat. No. 4,771,297 to Lecheheb. In such device, ink is supplied to the nozzle through an inlet 4 while the outlet 5 is normally closed to form a disk-like reservoir of ink in conduits 10/11 facilitating transmission of stimulated energy thereto. In the event of a clog, printing is interrupted for purposes of unclogging the nozzle orifice 17. Orifice 17 is formed in a removable cap 3 which is secured to protrusion 20 by a bayonet mounting. Clogs are manually cleared by removing the cap and, if necessary, flushing ink using the outlet or bleed port 5. This is done by connecting the outlet of the dual-port nozzle to either vacuum or atmospheric pressure to alternately suck air in through the orifice or pass ink across the mouth of the orifice to remove any debris or clogging material. This operation in which printing must be interrupted for unclogging, is desirably accomplished within an optimally short period of time.
In a related art, namely ink jet array printing, as exemplified in U.S. Pat. No. 4,591,873 to McCann et al. it is also known to use two ports. The flow across the array is necessary to create and maintain an ink reservoir for the array. In addition, it is known to alternate the urging of ink in the orifices from one side to the other, i.e., from the ink cavity to the exterior and then back (See McCann, Col. 6, lines 13-34). However, there is no teaching of how to sense the unclogging other than to initiate printing operation. This has not been used in the single continuous jet art because of increase in the drool problem and the greater supply required.
It is accordingly an object of the present invention to provide a cross flow nozzle and an improved anti-clogging system for a continuous jet, ink jet printer. More specifically, it is desired to provide an anti-clogging system which both lessens the possibility of clogging of the orifice and, when clogging occurs, to detect and clear the clog and return the printer to normal operation within an optimal period of time.
It is another object of the invention to provide a system of the type described which is highly reliable and capable of extended periods of operation without significant clogging or downtime resulting therefrom.
Another object of the invention is to provide an anti-clogging system for an ink jet printer which is capable of detecting a blockage in an ink jet printhead orifice to initiate unclogging thereof and then detecting removal of the blockage.
A further object of the invention is to provide ink jet nozzles of a type which are suitable for use with the anti-clogging system of the present invention. These and other objects of the invention will be apparent from the remaining portion of this specification.